Method of exhaust and apparatus therefor



Nov. 20, 1934- H. J. NOLTE METHOD OF EXHAUST AND APPARATUS THEREFORFiled April 14, 1930 70 R0067! PUMP lulu ImvenLor-w Henry J. Nolte, by Iwalk] His Attorney- Patented Nov. 20, 1934 UNITED STATES METHOD OFEXHAUST AND APPARATUS THEREFOR Henry J. Nolte, Schenectady, N. Y.,assigncr to General Electric Company, a corporation of New YorkApplication April 14, 1930, Serial No. 444,082

1 Claim.

The present invention relates to electric discharge apparatus and moreparticularly to the process of manufacturing certain types of suchapparatus.

In the manufacture of electric discharge tubes, it is necessary toremove occluded gases from the various metal parts within the envelopeand especially from such members, as the anode, which become heatedduring operation. The slightest amount of active gas given on by theanode or other metal member may impair the electrical characteristics ofthe tube and if sumcient gas is evolved, the resulting ionization underhigh voltage conditions may destroy the tube.

In order to overcome these difficulties and to ensure the release of thelast remnant of oceluded gas, it has been the practice heretofore toheat the metal members during the evacuation process by high frequencyor otherwise, to a temperature somewhat higher than that attained inoperation. This method gives satisfactory results in those cases wherethe heating of a given member can be effectively applied and where themember is sufl'iciently rugged to withstand the combined simultaneousheating and evacuating effects. However, certain forms of electricdischarge apparatus require members of hollow and delicate structure, asin the case of electrodes which are cooled during operation by anexternally applied medium such as water or air and must be thin in orderto ofier maximum ease of cooling.

The development of certain phases of the tube art has necessitated tubeswhich require electrodes of special configuration whose shape must berigidly maintained during the abnormal treatment given to the tube inmanufacture. Furthermore, for reasons of minimizing electricalresistance and oxidation as well as for other considerations, the metalof an electrode is usually copper. When such members are heated andimmersed in an attenuated atmosphere they are subject to deformation ofshape and sometimes collapse if the full atmosphere is allowed access tothe surface opposite to that being evacuated. Under these conditions thedifference in pressure exerted on opposite sides of the heated hollowmember constitutes a force tending to warp the soft material.

An object of my invention is to improve the technique of removingoccluded gases from electrodes and other metallic members of delicateconstruction contained in the envelope of electric discharge devices. Amore specific object is to improve the method of and apparatus forremoving occluded gases from electrodes of hollow'and thin construction,the outer surfaces of the electrodes being subjected to relatively highvacuum under operating conditions or manufacturing conditions, or both.A more general. object is to improve the manufacture of such devices.The invention will be better understood when reference is made to thefollowing description and the accompanying drawing in which Fig. 1 is aview partly in section and partly in elevation of a tube being evacuatedin accordance with my invention; Fig. 2 shows the anode constructionutilized in the tube illustrated in Fig. 1; Fig. 3 is a view partly insection of a cap arrangement fitted over one end of several exhaustconduits and useful in the evacuation of the anode interiors.

In Fig. 1, numeral 1 designates the glass envelope of a split anodemagnetically controlled discharge device which employs two semicircularmitten-like anodes 2, arranged symmetrically about an axially disposedfilament 3. A tube of this kind when connected in appropriate and knowncircuits and provided with electromagnetic coils 4 serves to generateoscillations of relatively large magnitude and of exceedingly short wavelengths for radio purposes. The anodes are constituted of thin copper,about 50 mils, and are peaned longitudinally at a position midway of thewidth as indicated at 5 in such a manner as to form a continuouspassage-way for a cooling medium along the upper, lower and end portionsof each member. However, during evacuation of the device and inaccordance with dicated), while the interior portion of each anodecommunicates with a rough pump (not shown but indicated) through one ofthe metal pipes or outlet conduits '7 and a metal hose 8. The adjacentmetal pipe or inlet conduit 9 which leads to the other portion of theanode interior is closedexcept for a small opening 10 drilledlongitudinally through a thumb-screw 11. The thumb-screw is threadedinto a metallic cylinder or cap 12 which embraces the pipe 9 and may besecured thereto by a set screw 13 or prefer- Q Wall.

During the evacuation, the filament 3 is energized and a high voltageapplied between the filament and each anode 2 whereby the latter isheated by electron bombardment to a temperature sufficiently high tofacilitate the removal of occluded gases. Inasmuch as the anode metal ishot during this operation and the copper wall is thin, the semi-circularanodes would normally tend to uncurl and straighten out if theatmosphere were allowed ready access to their interiors through'thepassage-ways during evacuation of the envelope.

However, in accordance with my invention, the pressure is maintainedsubstantially equal on both sides of the anode wall and there is no unbalanced force of appreciable amount present to blow out or otherwisedeform the shape of the anodes. The pump for maintaining the attenuatedatmosphere within the anode interior is V conveniently connected throughthe hose 8 to the metal tubing 7 by a rubber nipple 14 and it is foundthat the heat radiated by the anode during exhaust may deleteriouslyaffect the rubber. In order to maintain the rubber cool thereby toretain its pliability, it is necessary to cool the ends of the metaltubing to which the nipple is attached. This is conveniently done by theuse of water jackets 15 which have inlet and outlet ecuial.

trated this deformation may take the form of ports and are adaptedclosely to embrace the tubes 7 in a water-tight manner.

It will be evident that I have provided a convenient method andapparatus for removing the occluded gases from the metal of an electrodehaving a configuration and construction which would tend to deform whenheated and when the pressures of the gaseous mediums on opposite sidesof the electrode are substantially un- In the case of the type ofelectrode illusunrolling or straightening out when the pressure in theinterior of the electrode is considerably greater than that on theexterior thereof.

What I claimas new and desire to secure by Letters Patent'of the UnitedStates:

An electric discharge device comprising an envelope adapted to behermetically sealed and. containing a hollow electrode from which theoccluded gases are tobe removed, said electrode beingconstituted ofrelatively thin metal andv having a circular configuration which tendsto straighten out when the electrode is heated and when subjected toconsiderably greater pressure r in the interior than on the exteriorthereof, said electrode being adapted to be heated to a temperaturesufficiently high to facilitate the removal of the occluded gases, meansfor evacuating the interior of the envelope and simultaneously- Ioperating means for evacuating the interior of the hollow electrodewhereby the pressure on opposite sides of the electrode aresubstantially equalized, and whereby the normal configuration.

of the electrode is maintained under heated conditions, said lastmentioned means including inlet and outlet conduits'which communicatewith individual portions of the electrode interior, the inlet conduitbeing closed except for a small opening and the outlet being cooled by afluid jacket.

HENRY J. NOLTE.

